The article headline on the $446k renovation cost is very misleading. They did not spend that much on the $1 (which they actually payed 6,000 euro for). They ALSO bought the property next door for 22k euro and combine the two into a literal mansion with four bedrooms, two terraces, sauna, library etc etc etc. $446k for all that is super cheap.

edit: the last link is also a lie. They did not buy a 1 euro house, they bought a 10k euro house (presumably not part of the 1 euro program) and renovated it themselves.